1. Field of the Invention
The present invention relates generally to health equipment and, more specifically, to oxygen concentrators.
2. Description of the Related Art
Patients (e.g., those suffering with diseases such as emphysema, congestive heart failure, acute or chronic pulmonary insufficiency, etc.) may require supplemental oxygen. Other people (e.g., obese individuals) may also require supplemental oxygen, for example, to maintain elevated activity levels. Doctors may prescribe oxygen concentrators or portable tanks of medical oxygen for these patients. Usually a specific oxygen flow rate is prescribed (e.g., 1 liter per minute (LPM), 2 LPM, 3 LPM, etc.) Oxygen concentrators used to provide these flow rates may be bulky and heavy making ordinary ambulatory activities with them difficult and impractical. Portable tanks of medical oxygen may also be heavy and contain limited amounts of oxygen.
Oxygen concentrators may take advantage of pressure swing absorption. Pressure swing absorption may involve using a compressor to increase air pressure inside a canister that contains granules of a micro-porous mineral. As the pressure increases, certain air molecules may become smaller and may be absorbed into the micro-pores of the granules. An example of such a granule is found in certain volcanic ash. Synthetic granules (e.g., zeolite) may also be available in various granule and pore sizes. These granules may thus be used to separate gases of different molecular size (e.g., zeolite may be used to separate nitrogen and oxygen). Ambient air usually includes approximately 78% nitrogen and 21% oxygen with the balance comprised of argon, carbon dioxide, water vapor and other trace elements. When pressurized air is applied to the granules, nitrogen in the air may be absorbed in the micro-pores of the granules because of the smaller size of the nitrogen molecule. As the granules are saturated, the remaining oxygen may be allowed to flow through the canister and into a holding tank. The pressure in the canister may then be vented from the canister resulting in the previously absorbed nitrogen being released from the pores in the granules. A small portion of the bled oxygen may be used to further purge the nitrogen from the canister. The process may then be repeated using additional ambient air. By alternating canisters in a two-canister system, one canister can be collecting oxygen while the other canister is being purged (resulting in a continuous separation of the oxygen from the nitrogen). In this manner, oxygen can be accumulated out of the air for a variety of uses include providing supplemental oxygen to patients.
Prior art oxygen concentrators may have several limitations. For example, the compressor on the oxygen concentrator may be operated at a level required to meet the demands of the user regardless of the breathing rate of the user. In addition, the length of the supply tubing to the nasal cannula or mask from the oxygen concentrator may be limited to 6 to 8 feet. This limitation may be a problem for users using the device in their sleep. Prior art oxygen concentrators may also include a limited sensor and alarm to notify a user if the oxygen supplied by the oxygen concentrator is too low. Currently oxygen sensors in oxygen concentrators use a heated filament as a component. In addition, time, pressure and orifice size are used to determine a volume of air delivered to a user of an oxygen concentrator (however, this measurement technique may not account for pressure fluctuations).